The present invention relates broadly to a signal to noise ratio enhancement apparatus, and in particular to a digital integrating/auto-correlator apparatus.
In the prior art, various circuit arrangements have been utilized for improving signal detectability, especially in the presence of interfering noise or clutter signals. Moving target discriminating systems provide a greater degree of improvement in the signal-to-interference ratio by efficiently diminishing the effects of clutter signals which are caused by stationary reflectors, such as the earth's surface. The use of non-adaptive radar signal processors provide an acceptable clutter rejection for particular ranges and for particular types of clutter, but the performance of such systems degrades in an environment in which the clutter conditions are varying. Furthermore, when interfering clutter is not present, the conventional prior art non-adaptive processors are not generally optimum in the presence of ordinary electrical noise alone.
Matched filter signal processors have also provided a means for diminishing the effects of interfering clutter. However, many of these devices have not proven to achieve useful results under dynamically changing clutter conditions and in all range sectors. The defective results occur mainly in matched filter operation upon the echo returns from multiple-pulse burst transmission radar system. The matched filter processors fail to give the required signal interference cancellation. For example, when the target of interest lies in particular periods of the several interpulse periods of the multi-pulse burst, accurate cancellation does not occur. The results are randomly selective in that only in other particular interpulse periods may an acceptable signal-to-interference ratio be achieved. Thus, the total effect is the ultimate addition of the individual returns from a multiple-pulse burst to yield an output having a degraded signal-to-interference ratio.